Shared Price Calculation and Placement Recalculation

Context

Amounts appear on several surfaces before a sale is placed. Shared calculation avoids maintaining a separate display interpretation.

Decision

Quote, preview and placement share deterministic pricing, and placement always recalculates the amount it binds.

Alternatives Considered

Guarantee the previous preview within a tolerance. The recorded product direction binds the recalculated placement amount rather than a retained preview.

Maintain separate display and sale engines. Independent calculation paths would require ongoing parity work.

Consequences

Placement can return a changed amount with an explanation of the new calculation. Callers load inputs; the pure engine does not fetch data itself.